Error: Cannot find module "firebase"

Thats the Error I get, when i try to start my app.

image.png840x496 14.6 KB

app.component.ts:

import { Component } from '@angular/core';
import { Platform } from 'ionic-angular';
import { StatusBar } from '@ionic-native/status-bar';
import { SplashScreen } from '@ionic-native/splash-screen';
import {LoginPage} from "../pages/login/login";
import firebase from 'firebase';

@Component({
  templateUrl: 'app.html'
})
export class MyApp {
  rootPage:any = LoginPage;

  constructor(platform: Platform, statusBar: StatusBar, splashScreen: SplashScreen) {
    firebase.initializeApp({
      apiKey: "xxxx",
      authDomain: "xxxx.firebaseapp.com",
      databaseURL: "https://xxxx.firebaseio.com",
      projectId: "xxxx",
      storageBucket: "xxxxappspot.com",
      messagingSenderId: "xxxx"
    });

    platform.ready().then(() => {
      // Okay, so the platform is ready and our plugins are available.
      // Here you can do any higher level native things you might need.
      statusBar.styleDefault();
      splashScreen.hide();
    });
  }

}

package.json:

{
  "name": "quizapp",
  "version": "0.0.1",
  "author": "Ionic Framework",
  "homepage": "http://ionicframework.com/",
  "private": true,
  "scripts": {
    "clean": "ionic-app-scripts clean",
    "build": "ionic-app-scripts build",
    "lint": "ionic-app-scripts lint",
    "ionic:build": "ionic-app-scripts build",
    "ionic:serve": "ionic-app-scripts serve"
  },
  "dependencies": {
    "@angular/common": "4.1.3",
    "@angular/compiler": "4.1.3",
    "@angular/compiler-cli": "4.1.3",
    "@angular/core": "4.1.3",
    "@angular/forms": "4.1.3",
    "@angular/http": "4.1.3",
    "@angular/platform-browser": "4.1.3",
    "@angular/platform-browser-dynamic": "4.1.3",
    "@ionic-native/core": "3.10.2",
    "@ionic-native/splash-screen": "3.10.2",
    "@ionic-native/status-bar": "3.10.2",
    "@ionic/storage": "2.0.1",
    "ionic-angular": "3.4.2",
    "firebase": "^3.9.0",
    "ionicons": "3.0.0",
    "promise-polyfill": "6.0.2",
    "rxjs": "5.4.0",
    "sw-toolbox": "3.6.0",
    "zone.js": "0.8.12"
  },
  "devDependencies": {
    "@ionic/app-scripts": "1.3.7",
    "@ionic/cli-plugin-ionic-angular": "1.3.1",
    "typescript": "2.3.3"
  },
  "description": "An Ionic project"
}

I just tried to browse the forum but nothing helped making that app run.
How can I fix that issue?